1. Related U.S. Patent Applications
This is a continuation-in-part of U.S. patent application Ser. No. 08/265,326 entitled "Method And Apparatus For Multiplexing Voice And Data Over A Single Analog-Loop Telephone Line," filed Jun. 24, 1994, by Barry O'Mahony et al., and assigned to the assignee of the present invention.
2. Field of the Invention
The present invention relates to the field of Data Communication. More specifically, the present invention relates to data circuit terminating equipment's (DCEs) such as modems for transmitting voice and data over analog-loop telephone lines.
3. Prior Art
Current DCEs that support transmission of both voice and data over a single analog-loop telephone line typically implement the support in one of two approaches. Under the first approach, a DCE operates in one of two switchable modes, a voice mode and a data mode, whereas under the second approach, a DCE operates in a single continuous combined voice and data mode.
More specifically, under the first approach, both the calling and answering DCEs start out in the voice mode, where analog voice signals are bypassed from the transmitting telephone coupled to one of the DCEs onto the analog-loop telephone line, and similarly from the analog-loop telephone line to the receiving telephone coupled to the other DCE. While the DCEs are in voice mode, no data are transmitted by the DCEs on behalf of data transmitting equipment's (DTEs), such as computers, coupled to the DCEs at both end of the connection. To switch into the data mode, one of the DTEs would cause its DCE to transmit a predetermined signal pattern on its behalf. Upon detection of the predetermined signal pattern, the other DCE would acknowledge. If the acknowledgment is received by the initiating DCE within a predetermined time period, the DCEs would jointly establish a data transmission protocol, enter the data mode, and mute the DCE's voice path. The DTEs can now transmit data to each other through their respective DCEs and over the analog-loop telephone line. At the end of data transmission, the DTE that initiated the mode switching would cause its DCE to transmit another predetermined signal pattern on its behalf, return to the voice mode, and unmute the voice path. Likewise, upon detection of this other predetermined signal pattern, the other DCE would also forward the signal to its DTE, return to the voice mode, and unmute the voice path. Voice signals are once again bypassed from the transmitting telephone onto the telephone line, and from the telephone line to the receiving telephone.
Typically, the data transmission protocol jointly established by the calling and answering DCEs as an integral part of switching from the voice mode to the data mode is a High Level Data Link (HDLC) frame based type protocol.
Under the second approach, the DCEs always operate in a single continuous combined voice and data mode. The DCEs jointly establish a data transmission protocol at start up. The analog voice signals received from the coupled telephones are digitized by the DCEs or forwarded to the coupled DTEs for digitization. The DCEs transmit the digitized voice signals intermixed with the data received from the coupled DTEs. Conversely, the digitized voice signals received from the analog-loop telephone line are converted back into analog voice signals by the DCEs or forwarded to the coupled DTEs for conversion. The DCEs then forward the analog voice signals to the telephones.
Generally, the data transmission protocol jointly established by the calling and answering DCEs as an integral part of the initial start up of the single continuous combined voice and data mode is also a High Level Data Link (HDLC) frame based type of protocol. Except for "marking" the digitized voice to facilitate their identification and conversion back to analog voice signals, the digitized voice are otherwise handled as if they are data.
The first approach has the disadvantage that there is no voice communication between the connected parties during data transmission. Thus, DCEs implementing the first approach are really suitable only for applications where voice communication is unnecessary during data transmission or data transmission is merely required intermittently and for short duration.
The second approach has the disadvantage that the DCEs on both ends of the connection must support continuous combined voice and data mode. Therefore, for applications frequently involving "unacquainted" users, an initial phone call using "standalone" telephones directly coupled to another analog-loop telephone line must be made to establish the fact that such continuous combined voice and data call can be made between two DCE coupled telephones. Thus, DCEs implementing the second approach are really suitable only for applications involving primarily "acquainted" users.
With the continuing increase in the capabilities microprocessor based desktop computers, they are being applied to more and more applications that require simultaneous voice and data communications between two users. A particular example of these applications is personal conferencing where users at different sites cooperate orally and interactively with a shared workspace application on the creation or review of documents. Another example is remote technical support where the support engineers communicate orally with the users as well as interacting remotely with programs executing on the users'systems for diagnostic or demonstration purposes. Due to the disadvantages discussed above, neither types of DCEs serve these applications well. As a result, most users of these applications resort to two telephone lines, with one dedicated for voice communication, and the other dedicated to data communication.
Thus, it is desirable to be able to support multi-modal voice and data communication between two users over a single analog-loop telephone line that is more flexible and user friendly. U.S. patent application, Ser. No. 08/265,455, filed on Jun. 24, 1994, entitled Method and Apparatus for Making a Multi-Modal Voice and/or Data Call Over a Single Analog-Loop Telephone Line, discloses such method and apparatus. Under the disclosed method and apparatus, at least four modes, an idle mode, an analog voice mode, a digital data mode, and a simultaneous voice and data (SVD) mode are supported. It is also desirable then to be able to multiplex voice and data over the single analog-loop telephone line while operating in the SVD mode.
However, within a system that allows multiplexing of data and voice over a single analog loop telephone line, there often can be experienced a great deal of bandwidth devoted to "framing bits." Framing bits are required under certain communication protocols to indicate or differentiate between communication of certain types of data, for instance, voice information and non-voice or data information. During multiplexing of communication, when a particular type of data communication is interrupted or suspended, framing bits are required to close out the interrupted communication and more framing bits are required to start the next communication. Therefore, as the amount of multiplexing within a single analog loop line is allowed to increase, the amount of communication bandwidth taken up by framing bits increases and the overall effectiveness of the communication protocol to transmit and receive information (e.g., voice, or data) decreases. It would be desirable to provide a communication protocol that allows a large degree of multiplexing and high rates, yet still allows high bandwidth effectiveness. As will be disclosed in more detail below, the present invention provides for such method and apparatus that advantageously achieves these and other desirable results.
Accordingly, it is an object of the present invention to provide more effective communication within a single analog-loop telephone line. It is yet another object of the present invention to provide high bandwidth efficiency within a system allowing simultaneous voice and data (SVD) mode communication over a single analog-loop telephone line. To this end, it is further an object of the present invention to provide the above by reducing the amount of framing bits required when multiplexing between voice and data communications. These and other objects of the present invention not specifically stated above will become clear within discussions of the present invention herein.